The license for FCP allows you to install on any macs that you own and control.
I bought it in 2011, and I and my family have used it, legally, on perhaps a dozen difference macs since then. I'm currently on an M4 Pro MBP (released in November 2024).
That said, you should really consider whether you do want to purchase it. You may not get the same experience as you would on a more recent mac.
I suggest you try iMovie, which is free. Maybe it does all that you need.
Another alternative is DaVinci Resolve, which is also free and apparently less demanding in terms of OS versions. Some people use both Resolve and FCP. Resolve, even in the free version, is very powerful (though perhaps a bit less beginner friendly than FCP).